Spin-Orbit Torque Detection in Insulating Low-dimensional Magnets using scanning cryo-Sagnac Interferometry and spin-filter tunneling magnetoresistance

Detection and quantification of current-induced spin-orbit torques (SOT) in insulating magnetic materials remains a major challenge in the pursuit of efficient magnetic memory devices. We present two complementary methods for systematic detection of SOT in insulating van der Waals magnetic heterostructures: scanning cryo-Sagnac Kerr interferometry and spin-filter tunneling magnetoresistance (sf-TMR) measurement. Sagnac selectively couples to out-of-plane magnetic moments, enabling ultrasensitive detection of current-induced magnetic deflection due to SOT on magnets with both in-plane and perpendicular magnetic anisotropy. In addition, scanning Sagnac allows for micron-scale mapping of quasi-static domain textures, offering insight into the spatial distribution of both damping-like and field-like torques. Measurement of sf-TMR further serves as a sensitive tool for detecting relative spin canting between antiferromagnetic sublattices, with potential applications in detection of sublattice-selective SOT.